X-Ray Observations of Supernova Remnants as Distance Indicators
NAVAL RESEARCH LAB WASHINGTON DC
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SNRs are important in Galactic astrophysics because they are the major source of energy input to the interstellar medium, serve as the site of cosmic-ray acceleration and play a role in triggering star formation. Unlike H-II regions, whose distances can be constrained kinematically, Galactic SNRs have poorly determined distances. Of the currently known 180 Galactic remnants, only 15 have distance determinations and only a limited subset of these are likely to be reliable. Most methods of establishing distances to SNRs are either difficult and uncertain or are too inexact to be useful. We describe how soft X-ray observations, such as those made by the German X-ray observatory ROSAT, can be used to estimate distances to many shell-type SNRs. We have already applied this procedure to G326.3--1.8, and we apply it here to a number of SNRs with independently established distances in order to test the procedures validity.